1. Field of the Invention
The present invention relates to a works protecting system for use when AV data is transmitted and received between devices, and to a works protecting method therefor.
2. Description of the Related Art
AV data, which has been conventionally handled as analogue data by users, is handled as digital data in recent years resulting from the widespread use of digital satellite broadcasting, Internet transmission, DVDs, or the like. Additionally, the IEEE1394 high-speed serial bus capable of transmitting digital data at high speed has become practical. From the viewpoint of works protection, works protection systems for use when AV data is transmitted and received between devices are proposed.
For example, “Copy protect technologies in IEEE1394, integration with combined use of public key/common key”, Nikkei Electronics, 23 Mar., 1998, pp.47-53, describes a works protecting system comprising authenticating means and encrypting means. FIG. 1 shows the system in a block diagram and FIG. 2 in a state transition diagram. The configuration of the prior art works protecting system is as follows. When an AV data transmission direction is provided from a user to command input means 11 (S11), authenticating means 51 performs authentication through command control means 21 with authenticating means 141 on another party (S12). After the authentication, AV data transmitting means 31 starts transmission of AV data (S13). The AV data is encrypted at encrypting means 41 using a cryptographic key and transmitted to a transmission line through input/output means 61 In a transmitting-receiving device on another party, input/output means 111 receives the encrypted AV data from the transmission line. Decrypting means 131 decrypts the encrypted AV data using the cryptographic key and AV data receiving means 121 receives the decrypted AV data.
As is apparent from the above description, the prior art works protecting system performs authentication with a transmitting-receiving device on another party only after an AV data transmission direction is provided from a user, thereby having the disadvantage that it takes a long time before transmission of AV data.